A digital household electrical appliance such as a DVD has a storage unit using a flash memory for the purposes of holding a program for operating the equipment, storing processed data, and the like.
Flash memories are classified into serial flash memories such as NAND type flash memories and AND type flash memories, and NOR type flash memories, depending on the constructions of storage elements.
Among these flash memories, the NOR type flash memory is a highly reliable memory which has a low probability of defects occurring in writing or reading operation. Further, it can be directly accessed by a CPU, resulting in high reading speed and suitability for random access, and accordingly, it is often used as a memory for holding a program.
On the other hand, a serial flash memory has a relatively small size of a memory cell, i.e., about one-third of that of the NOR type flash memory. Further, it is highly integrated as well as has high erasing and writing speeds, i.e., it has an erasing time about one-hundredth of that of the NOR type flash memory and a writing time about one-twentieth of that of the NOR type flash memory.
However, a serial flash memory cannot be directly accessed by a CPU, and it has a relatively high probability of defects occurring in writing or reading operation. Therefore, such serial flash memory is utilized when storing data for which highly precise reading and writing are not required, as in cases when storing stream data having temporal continuity such as moving picture data and audio data.
From these functions and characteristics, in a conventional information processing apparatus for controlling the operations of conventional digital household electrical appliances, the NOR type flash memory is employed as a memory for holding a program. An information processing apparatus with a NOR type flash memory generally has a construction shown in FIG. 28. Hereinafter, the construction and operation will be described with reference to FIG. 28.
With reference to FIG. 28, a conventional information processing apparatus 100d has an information processing unit 30, a work memory 14 for holding variables, a NOR type flash 21 for holding a program, and an information saving unit 22 for saving information during power-down.
The work memory 14 is implemented by a SDRAM (Synchronous Dynamic Random Access Memory).
The NOR type flash 21 supplies stored data to the information processing unit 30 in response to an access from the information processing unit 30. Further, in response to an access from the information processing unit 30, it performs erasing of the stored data or storage of supplied data.
The information saving unit 22 is implemented by a SRAM (Static Random Access Memory) for holding management information such as operating states or disk writing addresses, which are supplied from the information processing unit 30. Because the SRAM has a relatively low power consumption, it can prevent the data stored in the SRAM from being erased even when the power is turned off, by using a backup battery. The information saving unit 22 holds the data without giving changes thereto until an erase/rewrite command is supplied from the information processing unit 30.
Next, the operation of the information processing apparatus 100d constructed as above will be described.
When power is applied to the information processing apparatus 100d, the information processing unit 30 reads out a variable stored in the information saving unit 22, and transmits the variable to the work memory 14. Then, the information processing unit 30 reads the program stored in the NOR type flash 21 for every step, and successively executes processing according to a command described in the program. When the variable varies, the information processing unit 30 rewrites the variable in the work memory 14. Further, the information processing unit 30 periodically performs, while executing the processing, back-up of the variable by storing the variable to the information saving unit 22. At turning off the power, the information processing unit 30 writes the status immediately before the turning-off of the power into the information saving unit 22.
However, because the memory capacity of the NOR type flash is about 32 Mbit at the maximum, it is becoming harder to store a program of a digital household electrical appliance in a single memory as the size of the program increases. On the other hand, providing plural NOR type flashes leads to an increase in the number of parts, resulting in an increased footprint as well as an increased manufacturing cost.
Further, the SRAM needs a backup power supply in order to retain the management information and the data immediately before turning off the power, even after the power is turned off. Therefore, the conventional digital household electrical appliances have circuits for continuously supplying power to the SRAM by a commercially available coin-shaped lithium battery or a rechargeable battery that is charged during power-on, resulting in a further increase in footprint. Moreover, since the SRAM itself is expensive, back up of management information that does not employ a SRAM is desired.
Furthermore, in the conventional information processing apparatus 100d, the information processing unit 30 reads a program from the NOR type flash 21, for every step, to execute processing, resulting in an extended execution time.
The present invention is made to solve the above-described problems and has for its object to provide an information processing apparatus, a memory management apparatus, a memory management method, and an information processing method, which can perform writing or reading of data into/from a serial flash memory having a large capacity with occurring no defects, and can reduce the CPU execution time by performing booting at power-on.